Ethylene is one of the main base products used in the petrochemicals industry, and it is used in the synthesis of products of great importance such as polyethylene, ethylene oxide, and many other products, either or not deemed to constitute commodities.
As a classical means of obtainment, ethylene is produced by way of thermal cracking of naphtha. This is a widely used process, both optimized and profitable, which however is hindered by the conceptual question of the use of petroleum in large amounts, being that this raw material is in itself a finite resource.
The replacement of petroleum with materials originating from renewable sources constitutes an essential point in the structuring of a new productive chain that may be environmentally sustainable. It is precisely within this context that there arise alternative methods for the production of ethylene, using sustainable obtainment means, in the so-called “green ethylene” line. One of these alternatives, which has proven to be quite successful to date, comprises the dehydration of ethanol obtained from the fermentation of natural carbohydrates, particularly the ethanol originated from the fermentation of sugarcane. The dehydration of this ethanol, also known as bio-ethanol, is a process that derives benefits from its high yield, the presence of a low amount of byproducts, the use of starting materials that are widely available and inexpensive, in addition to producing as a result a net reduction in the production of CO2 that is emitted to the environment.
The processes used to transform bio-ethanol into ethylene constitute an industrially attractive course for the manufacture of “green ethylene,” thus denominated due to using renewable sources, without requiring the consumption of petroleum derivatives.
Such processes, in industrial use, usually employ acid catalysts such as γ-Al2O3 and zeolite HZSM-5. Usually, the Al2O3 requires higher reaction temperatures (between 400 and 500° C.), while the use of zeolites of the HZSM-5 type allows the use of lower temperatures. Various other catalysts, such as silica-alumina, metal oxide, supported phosphoric acid and phosphate, may be used. However, the same acidity that facilitates the dehydration reaction leads to the formation of coke deposits and to the corresponding deactivation of the catalysts, thereby entailing an increase in operating costs inherent to the reactivation of these catalysts, or still worse, the substitution thereof. The presence of water in the starting ethanol reduces the deactivation caused by formation of coke, but increases the consumption of power and leads to the dealumination of the zeolites at high temperatures. The technical problem to be solved by the present invention is related to the high temperature that is required in the prior art processes to achieve the conversion of the alcohol to olefin.
Many studies have been conducted in terms of the research of alternative dehydration processes, and in this context there may be cited the use of carbon-based materials, in the presence of acids, with the surfaces thereof treated with oxidizers such as (NH4)2S2O8 and HNO3. Considerable improvements have been obtained with the treatment of various supports with sulfuric acid and phosphoric acid, however with the disadvantages brought about by significant limitations inherent to the high temperature of reaction and the intrinsic instability of the ethylene having been produced, of the byproducts in the production thereof, in the presence of such acid catalysts. This occurs due to the fact that with the use of sulfuric acid and phosphoric acid there is obtained a high selectivity for ether and a low selectivity for olefin.
As alternatives to the already known dehydration process, there arose dehydration processes using ionic liquids.
The ionic liquids based on imidazole are liquid organic compounds that have drawn much attention, both scientifically and technologically, due to their very peculiar properties, such as high stability, low (or null) volatility, different solubility with polar and non-polar compounds, high ionic and electrical conductivity, etc. In addition to these properties, that have found a role to ionic liquids as new solvents in various industrial processes, there may be further cited the high acidity evidenced by some of these materials. Such is the case in the olefin alkylation reactions.
U.S. Pat. No. 7,208,605 relates to the use of an IL [ionic liquid] with an appended acidic group for general or specific acid catalysis, either as a pure material, or as a solution in another ionic liquid or molecular solvent. Such reactions include, but are not limited to, Fischer esterification, pinnacol rearrangement, alcohol dehydration, rearrangements, isomerizations, Friedel-Crafts alkylation and acylation, or aromatic nitration.
US2009/0062571 discloses a process for dehydrating alcohols, polyalcohols and alcoholates having at least one CH group in the α position for the production of alkenes and ethers with ionic liquid. Among the ionic liquids used are the imidazole derivatives. Notwithstanding that the document teaches a process for the dehydration of alcohols in order to produce alkenes, there are only used higher alcohols in the process. The document does not suggest the use of ionic liquids for the dehydration of light alcohols in order to produce alkenes. It is known that the dehydration of light alcohols is rendered difficult by chemical factors (reactivity and kinetics).
The Chinese paper Dehydration of Ethanol Catalyzed by Acidic Ionic Liquid, of Gong Shengmin et al., (http://en.cnki.com.cn/Article_en/CJFDTOTAL-SYHG200901011.htm) discusses the dehydration of ethanol catalyzed by an acid ionic liquid. The document discloses the use of the ionic liquid 1-(4-sulphonic acid)butyl-3-methylimidazole hydrogen sulfate and sulfuric acid. The document discloses that the dehydration reaction occurs at a temperature that varies between 120 and 220° C., a high temperature that results in a considerable energy spending and impacts in olefin selectivity. Furthermore, the use of sulfuric acid is undesirable due to corrosion and its affinity for water, rendering difficult the separation of the water generated in the reaction. The use of ionic liquids comprising sulfur in their compositions is extremely undesirable due to the possible contamination of the resulting olefin.
US2009/0118558 discloses a process for dehydrating alcohols, for the purpose of producing olefins and/or ethers using an ionic liquid. The dehydration reactions occur at a temperature of 100 to 400° C. The ionic liquid used may be derived from imidazole. Also in this case, the process takes place at high temperatures, resulting in heavy energy costs. Furthermore, the process exhibits low selectivity for ethylene and formation of ether, and the conversion to ethylene mentioned in the examples is up to 12%. One disadvantage of this process is the fact that there is an additional step where the water needs to be condensed out from the olefin and/or ether product.
None of the above documents have mentioned high selectivity for producing olefins from light alcohols.
Therefore, in light of the problems presented in the prior art, the object of the present invention consists in the provision of a process for the dehydration of light alcohols intended for the production of olefins, with low generation of byproducts and reduced energy consumption, in addition to requiring a simple system for purifying the olefin having been generated, without requiring the addition of acids or other solvents in reaction. The process of dehydration of light alcohols is conducted at low temperature, thereby achieving high selectivity to olefins and requiring a purification process that is simple, due to the low rate of formation of impurities such as CO, H2, acetaldehyde and CO2.